Mirtazapine: a review of its clinical efficacy and tolerability

Brincidofovir inhibits polyomavirus infection in vivo

Polyomaviruses are species-specific DNA viruses that can cause disease in immunocompromised individuals. Despite their role as the causative agents for several diseases, there are no currently approved antivirals for treating polyomavirus infection. Brincidofovir (BCV) is an antiviral approved for the treatment of poxvirus infections and has shown activity against other double-stranded DNA viruses. In this study, we tested the efficacy of BCV against polyomavirus infection in vitro and in vivo using mouse polyomavirus (MuPyV). BCV inhibited virus production in primary mouse kidney cells and brain cortical cells. BCV treatment of cells transfected with MuPyV genomic DNA resulted in a reduction in virus levels, indicating that viral inhibition occurs post-entry. Although in vitro BCV treatment had a limited effect on viral DNA and RNA levels, drug treatment was associated with a reduction in viral protein, raising the possibility that BCV acts post-transcriptionally to inhibit MuPyV infection. In mice, BCV treatment was well tolerated, and prophylactic treatment resulted in a reduction in viral DNA levels and a potent suppression of infectious virus production in the kidney and brain. In mice with chronic polyomavirus infection, therapeutic administration of BCV decreased viremia and reduced infection in the kidney. These data demonstrate that BCV exerts antiviral activity against polyomavirus infection in vivo, supporting further investigation into the use of BCV to treat clinical polyomavirus infections.

IMPORTANCE

Widespread in the human population and able to persist asymptomatically for the life of an individual, polyomavirus infections cause a significant disease burden in the immunocompromised. Individuals undergoing immune suppression, such as kidney transplant patients or those treated for autoimmune diseases, are particularly at high risk for polyomavirus-associated diseases. Because no antiviral agent exists for treating polyomavirus infections, management of polyomavirus-associated diseases typically involves reducing or discontinuing immunomodulatory therapy. This can be perilous due to the risk of transplant rejection and the potential development of adverse immune reactions. Thus, there is a pressing need for the development of antivirals targeting polyomaviruses. Here, we investigate the effects of brincidofovir, an FDA-approved antiviral, on polyomavirus infection in vivo using mouse polyomavirus. We show that the drug is well-tolerated in mice, reduces infectious viral titers, and limits viral pathology, indicating the potential of brincidofovir as an anti-polyomavirus therapeutic.

A 9-year-old female with iron deficiency has severe periodic limb movements while taking mirtazapine for insomnia

Mirtazapine is a Food and Drug Administration-approved atypical antidepressant used off-label for insomnia. Mirtazapine has been associated with movement disorders in adults. A 9-year-old female was seen in the sleep clinic for symptoms of insomnia, nocturnal awakenings, restless sleep, and growing pains. Mirtazapine was started prior to presentation for severe insomnia. A sleep study showed frequent repetitive leg movements prior to sleep onset as well as significant periodic limb movement disorder with a periodic limb movement index of 25.1/hour. The child was found to have a ferritin level of 23 ng/mL and an iron saturation of 10%. There were concerns that the presence of iron deficiency along with the use of mirtazapine may have contributed to the elevated periodic limb movement index. After starting iron therapy to treat the child's iron deficiency, mirtazapine was weaned off, with further clinical improvements in sleep quality reported. A follow-up sleep study showed a resolution of her periodic limb movement disorder with a periodic limb movement index of 1.4/hour. This is the first pediatric case to describe a sleep-related movement disorder associated with the use of mirtazapine and polysomnographic data to support resolution after discontinuation of mirtazapine along with iron therapy.

CITATION

Hawkins M. A 9-year-old female with iron deficiency has severe periodic limb movements while taking mirtazapine for insomnia. J Clin Sleep Med. 2023;19(7):1369-1373.

Protective role of mirtazapine in adult female Mecp2+/- mice and patients with Rett syndrome

BACKGROUND

Rett syndrome (RTT), an X-linked neurodevelopmental rare disease mainly caused by MECP2-gene mutations, is a prototypic intellectual disability disorder. Reversibility of RTT-like phenotypes in an adult mouse model lacking the Mecp2-gene has given hope of treating the disease at any age. However, adult RTT patients still urge for new treatments. Given the relationship between RTT and monoamine deficiency, we investigated mirtazapine (MTZ), a noradrenergic and specific-serotonergic antidepressant, as a potential treatment.

METHODS

Adult heterozygous-Mecp2 (HET) female mice (6-months old) were treated for 30 days with 10 mg/kg MTZ and assessed for general health, motor skills, motor learning, and anxiety. Motor cortex, somatosensory cortex, and amygdala were analyzed for parvalbumin expression. Eighty RTT adult female patients harboring a pathogenic MECP2 mutation were randomly assigned to treatment to MTZ for insomnia and mood disorders (mean age = 23.1 ± 7.5 years, range = 16-47 years; mean MTZ-treatment duration = 1.64 ± 1.0 years, range = 0.08-5.0 years). Rett clinical severity scale (RCSS) and motor behavior assessment scale (MBAS) were retrospectively analyzed.

RESULTS

In HET mice, MTZ preserved motor learning from deterioration and normalized parvalbumin levels in the primary motor cortex. Moreover, MTZ rescued the aberrant open-arm preference behavior observed in HET mice in the elevated plus-maze (EPM) and normalized parvalbumin expression in the barrel cortex. Since whisker clipping also abolished the EPM-related phenotype, we propose it is due to sensory hypersensitivity. In patients, MTZ slowed disease progression or induced significant improvements for 10/16 MBAS-items of the M1 social behavior area: 4/7 items of the M2 oro-facial/respiratory area and 8/14 items of the M3 motor/physical signs area.

CONCLUSIONS

This study provides the first evidence that long-term treatment of adult female heterozygous Mecp2^tm1.1Bird mice and adult Rett patients with the antidepressant mirtazapine is well tolerated and that it protects from disease progression and improves motor, sensory, and behavioral symptoms.

Effect of mirtazapine on metabolism and energy substrate partitioning in healthy men

BACKGROUND

Weight gain and metabolic changes during treatment with antidepressant drugs have emerged as an important concern, particularly in long-term treatment. It is still a matter of ongoing debate whether weight gain and metabolic perturbations with antidepressant use are the consequence of increased appetite and weight gain, respectively, or represents direct pharmacological effects of the drug on metabolism.

METHODS

We therefore conducted a proof-of-concept, open-label clinical trial, hypothesizing that in exceptionally healthy men no change of metabolic parameters would occur under mirtazapine, when environmental factors such as nutrition, sleep, and physical exercise were controlled and kept constant. Over a 3-week preparation phase, 10 healthy, young men were attuned to a standardized diet adjusted to their individual caloric need, to a regular sleep/wake cycle and moderate exercise. Continuing this protocol, we administered 30 mg mirtazapine daily for 7 days.

RESULTS

While no significant weight gain or changes in resting energy expenditure were observed under these conditions, hunger and appetite for sweets increased with mirtazapine, accompanied by a shift in energy substrate partitioning towards carbohydrate substrate preference as assessed by indirect calorimetry. Furthermore, with mirtazapine, insulin and C-peptide release increased in response to a standardized meal.

CONCLUSION

Our findings provide important insights into weight-independent metabolic changes associated with mirtazapine and allow a better understanding of the long-term metabolic effects observed in patients treated with antidepressant drugs.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00878540.

FUNDING

Nothing to declare.

JC Polyomavirus Attachment and Entry: Potential Sites for PML Therapeutics

PURPOSE OF REVIEW

JC polyomavirus (JCPyV) is a significant human pathogen that causes an asymptomatic infection in the kidney in the majority of the population. In immunosuppressed individuals, the virus can become reactivated and spread to the brain, causing the fatal, demyelinating disease progressive multifocal leukoencephalopathy (PML). There are currently limited treatment options for this fatal disease. Attachment to receptors and entry into host cells are the initiating events in JCPyV infection and therefore an attractive target for therapeutics to prevent or treat PML. This review provides the current understanding of JCPyV attachment and entry events and the potential therapeutics to target these areas.

RECENT FINDINGS

JCPyV attachment and entry to host cells is mediated by α2,6-linked lactoseries tetrasaccharide c (LSTc) and 5-hydroxytryptamine receptors (5-HT₂Rs), respectively, and subsequent trafficking to the endoplasmic reticulum is required for infection. Recently, vaccines, monoclonal antibodies, and small molecules have shown promise as anti-viral and PML therapies.

SUMMARY

This review summarizes our current understanding of JCPyV attachment, entry, and trafficking and the development of potential PML therapeutics that inhibit these critical steps in JCPyV infection.

Occurrence and removal of frequently prescribed pharmaceuticals and corresponding metabolites in wastewater of a sewage treatment plant

The present study determines removal rates (RR) of 56 pharmaceuticals and metabolites, respectively, in an urban sewage treatment plant using mass flow analysis by comparing influent and effluent loads over a consecutive ten-day monitoring period. Besides well investigated compounds like carbamazepine and metoprolol, less researched targets, such as topiramate, pregabalin, telmisartan, and human metabolites of pharmaceuticals were included. Another aim was to determine the ratio of pharmaceuticals and corresponding metabolites in raw wastewater. Valsartan and gabapentin were detected at the highest average concentrations in influent (c(val) = 29.7 (± 8.1) μg/L, c(gab) = 13.2 (± 3.3) μg/L) and effluent (c(val) = 22.1 (± 5.1) μg/L, c(gab) = 12.1 (± 2.6) μg/L) samples. The comparison of mass loads in influent and effluent showed a significant removal (p<0.1) for 20 compounds but only enalapril, eprosartan, losartan, pregabalin, and quetiapine were removed from the aqueous phase by more than 50%. Another 20 compounds were determined without significant difference and for five compounds (clindamycin, lamotrigine, oxcarbazepine, O-desmethyl venlafaxine, triamterene), a significant higher mass load in the effluent than in the influent was observed. It has to be noticed that metabolites like 10,11-dihydro-10-hydroxy carbamazepine (MHD) are found in higher mass loads than the corresponding parent compound in the sewage samples. Furthermore, metabolites and parent compound behave differently in the sewage treatment process. While MHD (RR = 15.1%) was detected with lower mass load in the effluent than in the influent, oxcarbazepine (RR = -73.2%) showed the contrary pattern. When comparing expected and measured ratios of parent compound and metabolite in raw sewage, citalopram/N-desmethyl citalopram for example, showed good results. However, a major problem exists due to insufficient data regarding metabolism and excretion of many pharmaceuticals. This complicates the prediction of relevant metabolites and further efforts are needed to overcome this problem.

Efficacy and Tolerability of Generic Mirtazapine (Mirtax) for Major Depressive Disorder: Multicenter, Open-label, Uncontrolled, Prospective Study

OBJECTIVE

Mirtax is a generic mirtazapine widely used since 2003. We conducted an open-label, uncontrolled 6-week study to evaluate the efficacy and safety of Mirtax for major depressive disorder (MDD).

METHODS

Ninety three MDD patients with the diagnosis of MDD and 17-item Hamilton Depression Rating Scale (HDRS) score ≥14 were recruited. The HDRS, Montgomery-Åsberg Depression Rating Scale (MADRS), and the Clinical Global Impressions-Severity Scale (CGI-S) were administered at baseline, 1, 2, 4 and 6 weeks. Response (≥50% decrease in the HDRS or MADRS score), remission (absolute HDRS score ≤7 or MADRS score ≤10) and CGI-I score ≤2 were also calculated. Adverse event (AE) frequency and severity, weight, blood pressure, and pulse rate were checked to assess safety.

RESULTS

The starting dosage was 11.5±6.4 mg/day, and the maintenance dosage was 23.1±9.4 mg/day. During 6 weeks, HDRS, MADRS and CGI-S scores decreased from 25.1±5.6 to 11.9±8.6 (mean change -13.1±8.3, p<0.001), from 30.2±6.3 to 13.73±10.40 (mean change -16.5±9.8, p<0.001), and from 5.0±0.8 to 2.5±1.3 (mean change -2.5±1.3, p<0.001), respectively. The percentages of responders, remitters by HDRS and patients with a CGI-I score ≤2 were 64.6%, 35.4% and 52.7%, respectively. Significant decreases in HDRS, MADRS and CGI-S scores were confirmed at week 1. The total rate of AEs was 32.3%; the most frequently reported AEs were sedation (4.3%) and constipation (4.3%). Weight was increased from 58.8±10.6 to 60.3±9.3 kg (mean change 0.7±1.7 kg, p=0.004).

CONCLUSION

This study, as the first clinical trial of generic mirtazapine, demonstrated the efficacy and tolerability of Mirtax for MDD using a single treatment design.

Repeated administration of mirtazapine attenuates oxaliplatin-induced mechanical allodynia and spinal NR2B up-regulation in rats

Chemotherapic drugs may elicit acute or chronic peripheral neuropathies. Mirtazapine, as an antidepressant, is also used for the treatment of neuropathic pain. The current study aimed to investigate the effect of mirtazapine on the oxaliplatin-induced neuropathy in rats as well as the underlying mechanism. A neuropathy model was established in Sprague-Dawley rats by intraperitoneal (i.p.) injection of oxaliplatin 4 mg/kg twice a week for 4 weeks. The therapeutic potential of mirtazapine 10, 20, and 30 mg/kg/day per-orally for 28 consecutive days was evaluated. Subsequently, a dose of 1 mg/kg of WAY100635 i.p., a selective antagonist of 5-HT1A receptor, was preadministrated before mirtazapine 20 mg/kg/day per-orally in oxaliplatin-induced neuropathy. The behavioral tests and the expression of NMDA receptor subunit NR2B were determined. The results displayed that repeated administration of mirtazapine 20 or 30 mg/kg/day for 28 consecutive days significantly attenuated the mechanical allodynia and the up-regulation of spinal cord NR2B but not the cold hyperalgesia in rats with oxaliplatin-induced neuropathy, which was reversed by WAY100635 preadministration. Our findings suggest that oxaliplatin-induced mechanical allodynia is associated with spinal NR2B up-regulation, which may be attenuated by mirtazapine administration.

Efficacy and safety of mirtazapine in fibromyalgia syndrome patients: a randomized placebo-controlled pilot study

BACKGROUND

Data from an open-label trial suggest that mirtazapine might prove useful in treatment of fibromyalgia syndrome (FMS).

OBJECTIVE

To obtain preliminary efficacy data of mirtazapine for estimation of sample size requirements for a Phase 2 clinical trial in FMS.

METHODS

This 13-week randomized controlled trial compared the effects of mirtazapine 15 mg/day, mirtazapine 30 mg/day, and placebo in 40 patients with FMS. The primary outcomes were change in Pain Visual Analog Scale (PVAS) and proportion of pain responders (≥30% PVAS reduction). Secondary outcomes included scores from the Jenkins Sleep Scale (JSS), Patient Global Impression of Change (PGIC), Fibromyalgia Impact Questionnaire (FIQ), Hamilton Depression Rating Scale (HAM-D), Patient Global Assessment, and self-reported adverse events.

RESULTS

Significant within-group PVAS reductions from baseline were observed in all 3 groups, with the greatest improvement in the mirtazapine 30-mg group (p < 0.005); between-group difference was not significant. The proportion of pain responders did not meet significance criteria (66.67% for mirtazapine 30 mg, 50% for mirtazapine 15 mg, 41.67% for placebo). Significant within-group improvement in JSS scores was seen for mirtazapine 30 mg (p < 0.01) and mirtazapine 15 mg (p < 0.05). Between-group comparison achieved significance for JSS item 3, waking several times per night (p < 0.05). On the PGIC, 72.73% felt better with both mirtazapine dosages compared with 50% for placebo. Within-group FIQ responses indicated improvement in only mirtazapine-treated groups, whereas within-group improvement for HAM-D and Patient Global Assessment was observed in all groups. Based on our findings, the sample size requirement (80% power, 5% type I error) should be 83 per group to detect PVAS change difference between mirtazapine 30 mg and placebo. Common mirtazapine-related adverse events were increased appetite and weight gain.

CONCLUSIONS

Patients with FMS taking mirtazapine exhibited within-group significant improvement in most of the measured outcomes. Between-group analysis was predictably compromised by the small sample size. Mirtazapine was well tolerated. Further study with a larger sample size is likely to be useful.

Mirtazapine provokes periodic leg movements during sleep in young healthy men

STUDY OBJECTIVES

Recent evidence suggests that certain antidepressants are associated with an increase of periodic leg movements (PLMS) that may disturb sleep. So far, this has been shown in patients clinically treated for depression and in cross-sectional studies for various substances, but not mirtazapine. It is unclear whether antidepressants induce the new onset of PLMS or only increase preexisting PLMS, and whether this is a general property of the antidepressant or only seen in depressed patients. We report here the effect of mirtazapine on PLMS in young healthy men.

DESIGN

Open-labeled clinical trial (NCT00878540) including a 3-week preparatory phase with standardized food, physical activity, and sleep-wake behavior, and a 10-day experimental inpatient phase with an adaptation day, 2 baseline days, and 7 days with mirtazapine.

SETTING

Research institute.

PARTICIPANTS

Twelve healthy young (20-25 years) men.

INTERVENTIONS

Seven days of nightly intake (22:00) of 30 mg mirtazapine.

MEASUREMENTS AND RESULTS

Sleep was recorded on 2 drug-free baseline nights, the first 2 drug nights, and the last 2 drug nights. Eight of the 12 subjects showed increased PLMS after the first dose of mirtazapine. Frequency of PLMS was highest on the first drug night and attenuated over the course of the next 6 days. Three subjects reported transient restless legs symptoms.

CONCLUSIONS

Mirtazapine provoked PLMS in 67% of young healthy males. The effect was most pronounced in the first days. The possible role of serotonergic, noradrenergic and histaminergic mechanisms in mirtazapine-induced PLMS is discussed.

S32212, a novel serotonin type 2C receptor inverse agonist/α2-adrenoceptor antagonist and potential antidepressant: I. A mechanistic characterization

Although most antidepressants suppress serotonin (5-HT) and/or noradrenaline reuptake, blockade of 5-HT(2C) receptors and α(2)-adrenoceptors likewise enhances monoaminergic transmission. These sites are targeted by the urea derivative N- [4-methoxy-3-(4-methylpiperazin-1-yl)phenyl]-1,2-dihydro-3-H-benzo[e]indole-3-carboxamide (S32212). S32212 was devoid of affinity for monoamine reuptake sites, yet displayed pronounced affinity (pK(i), 8.2) for constitutively active human 5-HT(2CINI) (h5-HT(2CINI)) receptors, behaving as an inverse agonist in reducing basal Gα(q) activation, [(3)H]inositol-phosphate production, and the spontaneous association of h5-HT(2CINI)-Renilla luciferase receptors with β-arrestin2-yellow fluorescent protein. Furthermore, upon 18-h pretreatment, S32212 enhanced the plasma membrane expression of h5-HT(2CINI) receptors as visualized by confocal microscopy and quantified by enzyme-linked immunosorbent assay. Its actions were prevented by the neutral antagonist 6-chloro-5-methyl-N-[6-(2-methylpyridin-3-yloxy)pyridin-3-yl]indoline-1-carboxamide (SB242,084), which also impeded the induction by long-term exposure to S32212 of otherwise absent Ca(2+) mobilization in mouse cortical neurones. In vivo, S32212 blunted the inhibitory influence of the 5-HT(2C) agonist 2-(3-chlorobenzyloxy)-6-(1-piperazinyl)pyrazine (CP809,101) on ventrotegmental dopaminergic neurones. S32212 also blocked 5-HT-induced Gα(q) and phospholipase C activation at the h5-HT(2A) and, less potently, h5-HT(2B) receptors and suppressed the discriminative stimulus properties of the 5-HT(2A) agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane in rats. S32212 manifested marked affinity for human α(2A)- (pK(i) 7.2), α(2B)- (pK(i) 8.2), and α(2C)- (pK(i) 7.4) adrenoceptors, at which it abolished noradrenaline-induced recruitment of Gα(i3), Gα(o), adenylyl cyclase, and extracellular-regulated kinase1/2. Moreover, S32212 dose-dependently abolished the discriminative stimulus effects of the α(2)-adrenoceptor agonist (S)-spiro[(1-oxa-2-amino-3-azacyclopent-2-ene)-4,2'-(1',2',3',4'-tetrahydronaphthalene)] (S18616). Finally, S32212 displayed negligible affinity for α(1A)-adrenoceptors, histamine H(1) receptors, and muscarinic M(1) receptors. In conclusion, S32212 behaves as an inverse agonist at h5-HT(2C) receptors and as an antagonist at human α(2)-adrenoceptors (and h5-HT(2A) receptors). Its promising profile in preclinical models potentially relevant to the treatment of depression is described in J Pharmacol Exp Ther 340:765-780, 2012.

Platelet-derived serotonin links vascular disease and tissue fibrosis

Vascular damage and platelet activation are associated with tissue remodeling in diseases such as systemic sclerosis, but the molecular mechanisms underlying this association have not been identified. In this study, we show that serotonin (5-hydroxytryptamine [5-HT]) stored in platelets strongly induces extracellular matrix synthesis in interstitial fibroblasts via activation of 5-HT(2B) receptors (5-HT(2B)) in a transforming growth factor β (TGF-β)-dependent manner. Dermal fibrosis was reduced in 5-HT(2B)(-/-) mice using both inducible and genetic models of fibrosis. Pharmacologic inactivation of 5-HT(2B) also effectively prevented the onset of experimental fibrosis and ameliorated established fibrosis. Moreover, inhibition of platelet activation prevented fibrosis in different models of skin fibrosis. Consistently, mice deficient for TPH1, the rate-limiting enzyme for 5-HT production outside the central nervous system, showed reduced experimental skin fibrosis. These findings suggest that 5-HT/5-HT(2B) signaling links vascular damage and platelet activation to tissue remodeling and identify 5-HT(2B) as a novel therapeutic target to treat fibrotic diseases.

[11C]Mirtazapine binding in depressed antidepressant nonresponders studied by PET neuroimaging

RATIONALE

Lack of benefit from antidepressant drug therapy is a major source of human suffering, affecting at least 25% of people with major depressive disorder. We want to know whether nonresponse to antidepressants can be linked to aberrant neuroreceptor binding.

OBJECTIVE

This study aims to assess the antidepressant binding in brain regions of depressed nonresponders compared with healthy controls.

MATERIALS AND METHODS

Healthy volunteers and depressed subjects who had failed to benefit from at least 2 antidepressant treatments were recruited by newspaper advertisements. All subjects had received no antidepressant medication for at least 2 months before positron emission tomography (PET) that was carried out with [11C]mirtazapine. Kinetic parameters of [11C]mirtazapine were determined from PET data in selected brain regions by the simplified reference tissue model.

RESULTS

Binding potentials of [11C]mirtazapine in cerebral cortical regions were lower in depressed nonresponders than in healthy controls. Removal rates of [11C]mirtazapine were higher in diencephalic regions of depressed nonresponders than in healthy controls.

CONCLUSIONS

PET neuroimaging with [11C]mirtazapine showed aberrant neuroreceptor binding in brain regions of depressed subjects who had failed to benefit from treatment with antidepressant drugs.

Discriminative stimulus properties of the atypical antidepressant, mirtazapine, in rats: a pharmacological characterization

RATIONALE

Though interoceptive properties of antidepressants have been described, discriminative stimulus (DS) properties of mirtazapine, which does not affect monoamine reuptake, remain uncharacterized.

OBJECTIVES

The objectives of the study are to train rats to recognize a mirtazapine DS, then perform substitution studies with other antidepressants and drugs acting at sites occupied by mirtazapine.

MATERIALS AND METHODS

Using a two-lever, fixed-ratio 10 schedule, rats were trained to discriminate mirtazapine (2.5 mg/kg, i.p.) from saline.

RESULTS

Sessions, 63 +/- 8, were necessary to reach the criterion for 14 rats that all subsequently recognized (100%) mirtazapine at the training dose. Mirtazapine blocks serotonin (5-HT)(2C) receptors, and the 5-HT(2C) antagonists, SB242,084, SB243,213 and S32006, revealed dose-dependent and full (> or =80%) substitution at doses of 2.5, 2.5, and 0.63 mg/kg, respectively. By contrast, the 5-HT(2A) antagonists, MDL100,907 and SR46349-B, the 5-HT(2B) antagonist, SB204,741, and the 5-HT(3) antagonist, ondansetron, showed no significant substitution. Though mirtazapine indirectly recruits 5-HT(1A) receptors, the 5-HT(1A) agonists, buspirone and 8-OH-DPAT, did not substitute. Mirtazapine blocks alpha(2)-adrenoceptors, but several alpha(2)-adrenoceptor antagonists (yohimbine, RX821,002 and atipamezole) failed to substitute. Despite blockade by mirtazapine of histamine H(1) receptors, no substitution was seen with the selective H(1) antagonist, pyrilamine. Finally, the selective noradrenaline reuptake inhibitor, reboxetine (0.16), fully substituted for mirtazapine, whereas the 5-HT/noradrenaline reuptake inhibitors, duloxetine and S33005, several 5-HT reuptake inhibitors (citalopram, fluvoxamine, and paroxetine) and the dopamine reuptake inhibitors, bupropion and GBR12,935, did not substitute.

CONCLUSION

Mirtazapine elicits a DS in rats for which selective antagonists at 5-HT(2C) receptors display dose-dependent substitution, whereas drugs acting at other sites recognized by mirtazapine are ineffective.

Racemic intrathecal mirtazapine but not its enantiomers acts anti-neuropathic after chronic constriction injury in rats

The unique noradrenergic and specific serotonergic antidepressant mirtazapine acts antinociceptive. It is optically active and currently marketed as racemate. In an animal model of acute pain it has been shown that the enantiomers exhibit differential effects: the R(-)-enantiomer showed anti-, the S(+)-enantiomer pronociceptive properties while the racemate acted antinociceptive at low doses and profoundly pronociceptive after high-dose application. Aim of the present study was to evaluate potential enantioselective effects of mirtazapine in neuropathic pain. In a chronic constriction injury model of neuropathic pain, Wistar rats were injected (+/-)-mirtazapine and the enantiomers intrathecally. All substances were dosed between 0.001 and 1mg/kg and compared to vehicle in a randomized and blinded approach. Thermal hyperalgesia and mechanical allodynia were assessed. In contrast to the acute pain results, only racemic mirtazapine exerted significant sustained analgesic effects up to 48 h. Antinociception was observed at all dosages with a maximum in the range of 0.01 mg/kg. Surprisingly, neither enantiomer was pro- nor antinociceptive at any dose or time. Our findings suggest that the synergism of both enantiomers is required to evoke a significant analgesic effect for the treatment of neuropathic pain. Our study gained no evidence for the use of either R(-) nor S(+)-mirtazapine alone. Due to the unique characteristics of (+/-)-mirtazapine and its proven efficacy in acute pain our results suggest that racemic mirtazapine may be a particularly useful antidepressant in the adjunctive treatment of chronic neuropathic pain states and could provide additional benefit to current therapeutic options.

Dual- and triple-acting agents for treating core and co-morbid symptoms of major depression: novel concepts, new drugs

The past decade of efforts to find improved treatment for major depression has been dominated by genome-driven programs of rational drug discovery directed toward highly selective ligands for nonmonoaminergic agents. Selective drugs may prove beneficial for specific symptoms, for certain patient subpopulations, or both. However, network analyses of the brain and its dysfunction suggest that agents with multiple and complementary modes of action are more likely to show broad-based efficacy against core and comorbid symptoms of depression. Strategies for improved multitarget exploitation of monoaminergic mechanisms include triple inhibitors of dopamine, serotonin (5-HT) and noradrenaline reuptake, and drugs interfering with feedback actions of monoamines at inhibitory 5-HT(1A), 5-HT(1B) and possibly 5-HT(5A) and 5-HT(7) receptors. Specific subsets of postsynaptic 5-HT receptors mediating antidepressant actions are under study (e.g., 5-HT(4) and 5-HT(6)). Association of a clinically characterized antidepressant mechanism with a nonmonoaminergic component of activity is an attractive strategy. For example, agomelatine (a melatonin agonist/5-HT(2C) antagonist) has clinically proven activity in major depression. Dual neurokinin(1) antagonists/5-HT reuptake inhibitors (SRIs) and melanocortin(4) antagonists/SRIs should display advantages over their selective counterparts, and histamine H(3) antagonists/SRIs, GABA(B) antagonists/SRIs, glutamatergic/SRIs, and cholinergic agents/SRIs may counter the compromised cognitive function of depression. Finally, drugs that suppress 5-HT reuptake and blunt hypothalamo-pituitary-adrenocorticotrophic axis overdrive, or that act at intracellular proteins such as GSK-3beta, may abrogate the negative effects of chronic stress on mood and neuronal integrity. This review discusses the discovery and development of dual- and triple-acting antidepressants, focusing on novel concepts and new drugs disclosed over the last 2 to 3 years.

Neuroimaging of mirtazapine enantiomers in humans

INTRODUCTION

Mirtazapine is a racemic antidepressant with a multireceptor profile. Previous studies have shown that the enantiomers of mirtazapine have different pharmacologic effects in the brain of laboratory animals.

MATERIALS AND METHODS

In the present study, we used positron emission tomography (PET) and autoradiography to study effects of (R)- and (S)-[(11)C]mirtazapine in the human brain. Detailed brain imaging by PET using three methods of kinetic data analysis showed no reliable differences between regional binding potentials of (R)- and (S)-[(11)C]mirtazapine in healthy subjects.

RESULTS

Autoradiographic studies carried out in whole hemispheres of human brain tissue showed, however, that (R)- and (S)-mirtazapine differ markedly as inhibitors of [(3)H]clonidine binding at alpha(2)-adrenoceptors.

CONCLUSION

The multireceptor binding profiles of mirtazapine enantiomers, along with individual differences between subjects, may preclude PET neuroimaging from demonstrating reliable differences between the regional distribution and binding of (R)- and (S)-[(11)C]mirtazapine in the living human brain.

A brief review of antidepressant efficacy, effectiveness, indications, and usage for major depressive disorder

OBJECTIVE

Antidepressants treat major depressive disorder (MDD) with the burden of associated side effects and difficulties with compliance. The purpose of this article is to review the efficacy and effectiveness of antidepressants for MDD.

METHODS

The authors conducted a focused review of selected key issues and references relevant to the clinically relevant pharmacologic treatment of MDD. Principles of treatment are reviewed. Antidepressants reviewed include SSRIs, mixed norepinephrine or serotonin uptake inhibitors, dopamine or norepinephrine uptake inhibitors, norepinephrine uptake inhibitors, antidepressants with mixed properties, and monoamine oxidase inhibitors. Augmentation and psychotherapy strategies are reviewed.

RESULTS

Antidepressant efficacy has been established in randomized clinical trials and effectiveness studies for acute and long-term treatment, but many patients do not achieve remission. Augmentation strategies and focused psychotherapy can be helpful.

CONCLUSIONS

Antidepressants help most patients with MDD but some are resistant to treatment and have a difficult long-term course.

The effect of short-term, low-dose tricyclic and tetracyclic antidepressant treatment on satiation, postnutrient load gastrointestinal symptoms and gastric emptying: a double-blind, randomized, placebo-controlled trial

Antidepressants are commonly prescribed for patients with functional dyspepsia. However, the effect of tricyclic antidepressants on satiation and gastric emptying remains unclear, and there are no data for tetracyclic compounds. To compare the effects of nortriptyline (maximum dose: 50 mg daily) and mirtazapine (30 mg daily) vs placebo on gastric emptying, gastric satiation and postprandial symptoms after a nutrient load in healthy volunteers. Randomized, double-blind, placebo-controlled study evaluated gastric function before and after 14 days of nortriptyline (n = 13), mirtazapine (n = 13), or placebo (n = 14) in healthy volunteers. Validated methods were used to study gastric emptying ((13)C-octanoate) and satiation postnutrient drink test. The three arms were comparable with regard to age, gender, body mass index and hospital anxiety/depression scale. There were no statistically significant effects of mirtazapine or nortriptyline on gastric emptying compared to placebo (P = 0.34). Maximum tolerated volume was similar on drug and placebo (P = 0.56). Aggregate symptom score 30 min postmaximum tolerated volume after nutrient drink challenge on placebo was 132 (+/-21), vs 165 (+/-21) on mirtazapine, and 126 (+/-21) on nortriptyline 50 mg respectively (P = 0.28). Tricyclic and tetracyclic antidepressant agents do not appear to have significant effects on gastric motor or satiation postnutrient challenge in healthy individuals at the doses tested.

Mirtazapine improves sleep and lowers anxiety and depression in cancer patients: superiority over imipramine

GOALS OF THE WORK

This study aimed to compare the effectiveness of mirtazapine and imipramine on not only the distressing symptoms of cancer patients such as pain, nausea, vomiting, appetite loss, and sleep disturbances but also depressive and anxiety symptoms.

MATERIALS AND METHODS

Fifty-three patients with cancer who were diagnosed with major depressive disorder, anxiety disorder, or adjustment disorder were included. Twenty patients on mirtazapine, 13 patients on imipramine, and 20 patients in the control group without medication were interviewed during three visits (baseline, third week, and sixth week). Pain, nausea, vomiting, appetite loss, and sleep disturbances were evaluated with self-assessment single-symptom scales during each visit. The patients were also asked to complete the Hospital Anxiety Depression Scale (HADS) during each visit.

MAIN RESULTS

There were no significant differences among the three visits in the mirtazapine, imipramine, or control groups in terms of pain, nausea, vomiting, or appetite loss. For the initial, middle, and late insomnia, only the mirtazapine group showed improvements (p = 0.001, p = 0.001, p = 0.003). There were also significant differences in the mean total (p = 0.03), anxiety (p = 0.003), and depression (p = 0.025) scores of HADS among the three visits for patients taking mirtazapine. There were no significant differences for HADS scores from the baseline to the end point for patients taking imipramine or control group patients.

CONCLUSION

Our findings suggest that mirtazapine is effective for resolving insomnia as well as anxiety and depressive symptoms in cancer patients. However, more systematic research, such as placebo-controlled studies, is needed.

Receptor occupancy of mirtazapine determined by PET in healthy volunteers

RATIONALE

Molecular tools are needed for assessing anti-depressant actions by positron emission tomography (PET) in the living human brain.

OBJECTIVES

This study determined whether [(11)C]mirtazapine is an appropriate molecular tool for use with PET to estimate the magnitude of neuroreceptor occupancy produced by daily intake of mirtazapine.

METHODS

This study used a randomised, double-blind, placebo-controlled, parallel-group, within-subject design. Eighteen healthy volunteers were PET-scanned twice with [(11)C]mirtazapine; once under baseline condition and again after receiving either placebo or mirtazapine (7.5 or 15 mg) for 5 days. We determined kinetic parameters of [(11)C]mirtazapine in brain regions by the simplified reference region method and used binding potential values to calculate receptor occupancy produced by mirtazapine.

RESULTS

Serum concentrations of mirtazapine ranged from 33 to 56 nmol/l after five daily doses of 7.5 mg mirtazapine and were between 41 and 74 nmol/l after 15 mg mirtazapine. Placebo treatment failed to alter the binding potential of [(11)C]mirtazapine from baseline values, whereas daily intake of mirtazapine markedly decreased the binding potential in cortex, amygdala and hippocampus. Receptor occupancy ranged from 74 to 96% in high-binding regions of the brain after five daily doses of 7.5 mg or 15 mg mirtazapine, whereas 17-48% occupancy occurred in low-binding regions.

CONCLUSIONS

[(11)C]Mirtazapine together with PET can determine the degree of receptor occupancy produced by daily doses of mirtazapine in regions of the living human brain.

Discriminative stimulus properties of the selective norepinephrine reuptake inhibitor, reboxetine, in rats: a characterization with alpha/beta-adrenoceptor subtype selective ligands, antidepressants, and antagonists at neuropeptide receptors

Although little information is available concerning discriminative stimulus (DS) properties of antidepressants, rats can be trained to recognize the selective norepinephrine (NE) reuptake inhibitor, reboxetine (2.5 mg/kg i.p.). By analogy to reboxetine (effective dose50, 1.1), 'full' (80%) substitution dose50 was obtained with the NE reuptake inhibitors, nisoxetine (4.9), nomifensine (0.5) and BW1555,U88 (1.0). Full substitution was also attained with the NE/serotonin (5-HT) reuptake inhibitors, S33005 (0.3), venlafaxine (4.8) and duloxetine (26.8), and the tricyclics, imipramine (2.5) and clomipramine (2.9). In contrast, the 5-HT reuptake inhibitors, citalopram, sertraline and paroxetine (all >2.5), and the 5-HT reuptake inhibitors/5-HT2 receptor antagonists, nefazodone and trazodone (both >10.0), did not substitute for reboxetine. The 'atypical' antidepressants, mirtazapine (>10.0) and mianserin (>2.5), similarly failed to substitute. DS properties of reboxetine were dose-dependently blocked by the alpha1-adrenoceptor (AR) antagonists, prazosin (inhibitory dose50, 0.3) and WB4101 (0.5), but resistant to the alpha2-AR antagonists, atipamezole (>0.63), idazoxan (>2.5) and RX821,002 (>0.08), and to the beta1-AR and beta2-AR antagonists, betaxolol (>2.5) and ICI118,551 (>10.0). Interestingly, the neurokinin-1 receptor antagonist, GR205,171, stereospecifically substituted for reboxetine (1.1) compared to its less active isomer, GR226,206 (>10.0). The corticotrophin-releasing factor-1 antagonists, DMP695 (>40), CP154,526 (>10.0) and SN003 (>40.0), and the melanin-concentrating hormone-1 antagonist, SNAP-7941 (>40.0), failed to substitute for reboxetine. In conclusion, DS properties of reboxetine are mimicked by antidepressants recognizing NE transporters, and require functionally intact alpha1-ARs for their expression. The neurokinin-1 antagonist, GR205,171, mimics the interoceptive properties of reboxetine, possibly reflecting its elevation of extracellular levels of NE in corticolimbic structures.

Antidepressants in the treatment of fibromyalgia

Fibromyalgia syndrome is a chronic disease of widespread and debilitating pain whose cause is unknown and whose risk factors are poorly understood. It is often comorbid with rheumatoid and other pain disorders as well as psychiatric disorders such as anxiety and depression. Although they are not officially approved for this indication, antiepileptics and antidepressants are often used to treat fibromyalgia. The tricyclic antidepressants (TCAs), particularly amitriptyline, are among the most common treatment strategies. Because of the poor tolerability of the tricyclics, the newer antidepressants have been widely tested in fibromyalgia. The selective serotonin reuptake inhibitors (SSRIs) and the reversible monoamine oxidase inhibitors do not seem to be particularly helpful. The serotonin and norepinephrine reuptake inhibitors (SNRIs), duloxetine and milnacipran, on the other hand, have been shown in placebo-controlled trials to offer significant relief to patients suffering from fibromyalgia. Although no direct comparative studies have been performed, these compounds appear to be as effective as the TCAs but much better tolerated. The effectiveness of the SNRIs as well as other dual acting antidepressants, such as mirtazapine, but not the SSRIs, implies that a dysfunction of both serotonin and norepinephrine neurotransmission probably exists in fibromyalgia. The effectiveness of antidepressants appears to be independent of their effect on comorbid depression.

PET neuroimaging of [11C]mirtazapine enantiomers in pigs

Previously, we used positron emission tomography (PET) for studying the pharmacokinetics of rac-[11C]mirtazapine in living brain. Our findings showed that rac-[11C]mirtazapine has suitable properties for PET neuroimaging. However, separate studies of enantiomers are typically required for characterizing the pharmacokinetics of a racemic drug. Therefore, we have determined the whole-body distribution and brain pharmacokinetics of S- and R-[11C]mirtazapine in pigs. The enantiomers of [11C]mirtazapine produced similar effective doses of radioactivity in most body organs, except for the brain, in which the dose was approximately 40% higher after injection of S-[11C]mirtazapine than the antipode. Kinetic analyses of dynamic brain PET recordings showed that values for regional accumulation of compound (k3) were significantly higher for S-[11C]mirtazapine than for the antipode, while the values for clearance of compounds from tissue to circulation (k2) were consistently lower for S-[11C]mirtazapine than for the R-form. No reliable difference occurred in the rate of metabolism of S- and R-[11C]mirtazapine in the bloodstream of the pigs. The present findings indicate that enantioselective processes affect the cerebral pharmacokinetics of rac-mirtazapine.

Mirtazapine and its enantiomers differentially modulate acute thermal nociception in rats

The antidepressant mirtazapine is an optically active drug and currently marketed as a racemic compound consisting of its S(+) and R(-)-enantiomers in a 50:50 mixture. As stereochemistry of antidepressants has become increasingly important to consider for the relevance of their analgesic properties, we investigated the effect of (+/-)-mirtazapine and its enantiomers in an animal model of acute thermal nociception. Wistar rats were injected intrathecal with either (+/-)-mirtazapine, R(-)-mirtazapine, S(+)-mirtazapine from 1 to 0.001 mg/kg and vehicle (0.9% NaCl), respectively. The effects on thermal paw withdrawal thresholds were monitored using the Hargreaves test. (+/-)-Mirtazapine exerted pro- and antinociceptive effects in acute thermal nociception, whereas R(-)-mirtazapine showed solely antinociceptive and S(+)-mirtazapine pronociceptive properties. These results clearly demonstrate a differential effect of (+/-)-mirtazapine and its enantiomers on nociception. As R(-)-mirtazapine exerts the antinociceptive activity of the racemic mixture it may be a putative candidate for an enantioselective use as analgesic.

The effect of mirtazapine in patients with chronic pain and concomitant depression

OBJECTIVE

To evaluate the safety, tolerability and efficacy of mirtazapine in patients with the primary diagnosis of chronic pain and concomitant depression in an open post-marketing surveillance study.

RESEARCH DESIGN AND METHODS

594 patients with a primary diagnosis of at least one chronic pain syndrome (minimum duration of 3 months) and the diagnosis of concomitant depression, appropriately made by a neurologist or psychiatrist, were recruited at psychiatric and/or neurological outpatient facilities throughout Germany. The primary efficacy parameter was pain at baseline and endpoint using a patient self-assessment scale. Secondary analyses were performed at baseline, week 1 (day 7 +/- 2), week 4 (day 28 +/- 4) and at endpoint (day 42 +/- 4 or early termination) and included safety and tolerability assessments. Investigators rated the severity of different potential co-morbidities (including depression) with a four-step rating scale (not present, mild, moderate, severe).

RESULTS

594 patients were enrolled and treated with mirtazapine (mean daily dose of 34.5 +/- 10.4 mg at study endpoint). A statistically significant (p < 0.0001; one sample sign test) reduction of pain from baseline to endpoint was found for the overall population. The percentage of patients free of pain or with only moderate pain increased significantly, irrespective of patients' age or pain syndromes. Furthermore, we found a substantial improvement from baseline to endpoint regarding co-morbidities such as sleep disturbance, irritability and exhaustion. The number of adverse events was low (<7%; n = 37), with fatigue (n = 13) and weight gain (n = 11) occurring most frequently. No previously-unknown side effects occurred. One hundred and six patients (18%) discontinued mirtazapine during the study. The main reason was lack of efficacy (6%, n = 33), which may be a reflection of sub-optimal response to the anti-depressant or analgesic effect of the drug, but no appropriate rating scale was used to clarify this question. Only a small number of patients stopped the drug due to adverse events (3%; n = 15). At study endpoint, the majority of physicians and patients rated the overall efficacy and tolerability of mirtazapine as good or very good. Most patients (80%) continued the therapy after 6 weeks.

CONCLUSIONS

Despite the limitations of an open observational study, our findings suggest that mirtazapine is a safe and well-tolerated drug for use in daily clinical practice. It still remains unclear whether the reduction of pain, the enhancement of the depressed mood or the combination of both effects led to these results. Nevertheless, our data point to a potential beneficial effect of mirtazapine in the treatment of patients with pain and concomitant depression. However, more systematic research, including placebo-controlled studies, and further empirical testing are necessary.